POLYPODIUM POLYSTICHUM. 195 



Thomson's attention to it, and lie promised to separate that 

 part, to try if the dentation would be permanent. Another 

 variety is in cultivation, named P. v. bifidum (Twice-cut) 

 that is, with the apex of each pinna divided into two parts, all 

 the other parts remaining the same as the common one. All 

 these are readily increased by dividing the creeping rhizomes. 

 P. v. omnilacerum (All -cut), is another very distinct and 

 beautiful form of this species. All the divisions are lengthened- 

 out and toothed along the margin. There is also a crested 

 form of the Polypody, called cristatum. 



POLYSTICHUM. 



A large assemblage of Ferns, . separated from Aspidium by 

 M. Schott, a German botanist. The distinguishing characters 

 of this genus consist in round spore-masses, with round cover, 

 and leathery, thick, spiny fronds, and a certain rigidity of 

 habit. Many well-known Ferns are included in this genus. 

 The hardy ones are 



POLYSTICHUM ACEOSTICHOIDES (Acrostichum-like). A 

 North- American Fern of great beauty. It has the advantage, 

 also, of being evergreen that is, the fronds do not die-off in 

 autumn. Fronds lance-shaped, 2 feet high, and pinnated : the 

 leaflets are narrow, with short stalks, with long spiny hairs. 

 Spore-masses on the upper part of the frond, where it con- 

 tracts. Stalks scaly. Eootstock tufted: hence it is slow to 

 increase by division. 



P. ACULEATUM (Thorny Fern). A British Fern, and also 

 found in every quarter of the globe. Fronds 2 feet high, 

 broad, lance-shaped, bipinnate ; pinnules dark green, rigid 

 and thorny, the one nearest the base generally the largest. 

 Spore-masses thickly placed on the upper part of the frond. 

 Stalks thickly covered with brown scales. Eootstock tufted. 

 Increased by dividing large many- tufted plants. Common on 

 hedgebanks about Burnham Beeches, in Buckinghamshire, and 



